Short period fluctuations in the characteristics of wireless echoes from the ionosphere

A new experim ental techn ique is described for study ing th e d irectional an d po larization characteristics of wireless echoes. The m ethod m akes use of an o rd inary spaced fram e direction-finding system , com bined w ith a tw inchannel am plifier an d ca thode-ray tu b e , so th a t by observations of an ellipse on th e screen th e phases an d am plitudes of th e e.m .f.s in th e aerial system m ay be determ ined . B y ap p ro p ria te connexions of th e aerials e ither of th e tw o characteristics m entioned m ay be studied . The equ ipm ent is m ade applicable to pulse transm issions by m eans of an 4 echo selecting ’ device, w hich has th e function of desensitizing th e a p p a ra tu s for all b u t a sm all elem ent of th e tim e-base cycle. The d u ra tio n of th e active period is of th e order of 15/^sec., an d by m eans of su itab le phasing circu its i t m ay be m ade to coincide w ith th e arrival of any echo of th e pulse p a tte rn , causing th e ellipses ap p ro p ria te to th a t elem ent to ap p ear alone on th e ca thode-ray tu b e screen. In po larization m easurem ents a single ellipse is produced on th e screen corresponding to th e e.m .f.s in tw o loops a t rig h t angles. In d irectional m easurem ents, th e aerials &re sw itched a t 25 eye./sec. by relays so th a t tw o ellipses are p roduced, one rep resen ting th e phase difference in one p a ir of spaced fram es, and th e o ther th a t in th e o ther pair. These are separa ted la tera lly on th e tu b e by a synchronized m agnetic deflecting circuit. The figures are pho tographed on a m oving film, an d th e ellipses due to each pulse from th e tra n sm itte r are th u s recorded separate ly . In th is w ay rap id changes in po larization and direction can be stud ied . The m ethod has been applied to th e various types of ionospheric echo, and records are show n to illu stra te th e ir behaviour. In p a rticu la r it has been used to s tu d y th e short-lived sc a tte r echoes ob ta ined on high pow er transm issions, whose characteristics change too rap id ly to be followed by m anual m ethods. The resu lts of b o th po larization and directional m easu re­ m en ts are considered in re la tion to th e general p roblem of ionospheric irregularities.